Programme

L.10.2 -- Lecture, ANSWCCMS-2023

Date: Thursday, 9 November 2023

Time: 17:00 - 18:00

Simulations of Single and Two-Particle Excitations: From Many-Body Perturbation Theory to The Spectral Density Functionals

Nguyen Ngoc Linh

Faculty of Materials Science and Engineering, Phenikaa University

Understanding the single and two-particle excitation properties of materials is pivotal for the accurate interpretation and prediction of optical spectroscopy in experimental measurements. This necessitates robust computational approaches, often rooted in many-body perturbation theory employing Green's functions (GW) and the resolution of Bethe-Salpeter equations (BSE). In the first part of my talk, I will present an overview of recent advancements in the efficiency of GW and BSE solutions. By leveraging density functional perturbation theory and a localized orbital representation, these developments are tailored to address large-scale systems encompassing up to a thousand electrons. Through a series of compelling examples, including heterogeneous and nanostructures, as well as disordered systems that traditionally pose challenges to conventional methodologies, I will showcase the marked efficiency gains achieved. In the second part, I will introduce a recent groundbreaking development, termed Koopmans-compliance functionals. These functionals are defined to enforce piecewise linearity and ensure the correct discontinuity derivative in energy functionals concerning fractional occupation, specifically in the context of charged excitations. The implications of this development are profound, enabling precise simulations of single-particle properties such as the photoemission spectrum of molecules, exhibiting an outstanding concordance with experimental ultraviolet photoemission spectroscopy. Moreover, these functionals yield accurate band gaps and band structures of semiconductors, aligning closely with GW-derived results.

Presenter: Nguyen Ngoc Linh